This invention relates to a process and system for drying moisture-laden feedstock materials through the use of solvent vapors which form an azeotrope with water. More specifically, this invention relates to a process which can dry a continuous stream of moisture-laden feedstock.
One fundamental process common to a wide range of industries is the drying of a feedstock to be subjected to further processing or uses. The feedstock can be of the type to be burned or processed to release energy such as carbonaceous products and municipal refuge, feedstocks which require drying for reactivation or other further processing, such as ion exchange resins, and feedstocks which will be subjected to further processing so as to be incorporated in a compound or processed product, such as wet pulp materials. Characteristically, drying these feedstocks by simple application of heat is so expensive and time consuming as to be practically and economically impossible.
Accordingly, various industries have adopted a number of solutions to the problem. One solution practiced widely in the carbonaceous products industries is the combination of a combustion feedstock, e.g., coal, with a solvent which, upon the application of heat, will form an azeotrope with the moisture in the feedstock, which can be flashed or evaporated off at substantially lower temperatures than simple heat-applied drying would require. U.S. Pat. No. 4,212,112 is an example of just such a process, which employs benzene as the solvent. However, this patent, which is characteristic of the art in general, a process which requires first mixing the feedstock, coal, and the organic solvent, benzene, in a liquid state to form a slurry, and thereafter applying heat to the formed slurry, subsequently separating off the vapor and the feedstock and recycling. This process is however, disadvantageous in a number of respects.
First, the process requires the separate steps of the formation of a slurry prior to the evaporation of the azeotrope and further processing, requiring two independent steps. it would be far more economical, and advantageous, to employ a process which operated on a continuous feedstock stream, as this would require less handling, less machinery, and be capable of far greater processing capability.
Second, the process of U.S. Pat. No. 4,212,112, as well as a related process for drying wood, described in U.S. Pat. No. 3,094,431 are feedstock-specific, that is, they are applicable to drying of only one type of feedstock, for a single end purpose.
Third, most of the processes, including the processes of the above-referenced patents, require downstream processing to separate the feedstock from the solvent remaining therewith, in a dried slurry. This further increases the cost, and limits the processing capacity, of the system.
Accordingly, it is one object of this invention to provide a drying process which overcomes the above-described disadvantages.
It is another object of this invention to provide a drying process which dries a continuous stream of feedstock, without separated mixing steps.
It is a further object of this invention to provide a drying process which is not feedstock-specific, and can be applied to a wide range of moisture-laden feedstock types.
It is yet another object of this invention to provide a process which delivers the dried feedstock in an essentially solvent-free condition, not requiring further processing for the removal of the solvent.